Device for inspecting element substrates and method of inspecting element substrates using electromagnetic waves

ABSTRACT

A detector substrate is provided adjacent to an element substrate to inspect any defect in a semiconductor element and a wiring formed on the element substrate. An electromagnetic wave is irradiated to a gas provided between the detector substrate and the element substrate to ionize the gas. An electric current between the detection substrate and the element substrate through the ionized gas is measured by an ammeter for a video signal for displaying white. Also, an electric current between the detection substrate and the element substrate through the ionized gas is measured by an ammeter for a video signal for displaying black. A ratio of these electric currents is obtained as a ratio of white and black. An element substrate having quality lower than a reference quality is removed as defective.

This application is a DIV of Ser. No. 09/866,651, filed on May 30, 2001,now U.S. Pat. No. 6,729,922.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a device for inspecting whether a pixelportion properly operates prior to forming an EL (electroluminescence)element in a light-emitting device in which the EL element is formed ona substrate and to a method of inspection. The EL (electroluminescent)devices referred to in this specification include triplet-based lightemission devices and/or singlet-based light emission devices, forexample. More particularly, the invention relates to a device forinspecting whether the pixel portion properly operates prior to formingan EL element in a light-emitting device that uses a semiconductorelement (using a thin semiconductor film), to a method of inspection, toa method of fabricating the light-emitting device that incorporates theinspection method in one of the fabrication steps and to thelight-emitting device fabricated by using the above fabrication method.

The EL element according to this invention has a structure in which anEL layer is sandwiched between a pair of electrodes. The EL layer standsfor a layer containing an organic compound that emits fluorescent lightor phosphorescent light upon the application of an electric field.

The light-emitting device to be inspected by the inspection device ofthis invention stands for an image display device or a light-emittingdevice using an EL element. Further, the light-emitting deviceencompasses all of those modules in which a connector such as ananisotropic electrically conducting film (FPC: flexible printedcircuit), a TAB (tape automated bonding) tape or a TCP (tape carrierpackage) is attached to the EL element, modules in which a printedwiring board is provided at an end of the TAB tape or the TCP, or themodules in which an IC (integrated circuit) is directly mounted on theEL element by a COG (chip-on-glass) system.

2. Description of the Prior Art

In recent years, technology has been greatly advanced concerning formingTFTs (thin-film transistors) on a substrate, and attempts have been madeto apply the technology to the active matrix display devices(light-emitting devices). In particular, the TFT using a polysiliconfilm exhibits a field-effect mobility (also called mobility) which ishigher than that of the conventional TFT using an amorphous siliconfilm, and makes it possible to accomplish a high-speed operation. Thismakes it possible to control the pixels that had been controlled by adrive circuit outside the substrate by using a drive circuit formed onthe same substrate as the pixels.

In the active matrix light-emitting device, various circuits andelements are formed on the same substrate to obtain various advantagessuch as decreasing the cost of production, decreasing the size of theelectro-optical device, increasing the yield and decreasing thethroughput.

Further, study has been vigorously forwarded concerning the activematrix light-emitting device (inclusive of EL display) having an ELelement as a self-light-emitting element. The light-emitting device isalso called an organic EL display (OELD) or an organic light-emittingdiode (OLED).

The EL element possessed by the light-emitting device has a structure inwhich the EL layer of an organic compound is sandwiched between a pairof electrodes (cathode and anode). Here, however, the EL layer usuallyhas a laminated-layer structure. A representative example may be alaminated-layer structure of “positive hole-transportinglayer/light-emitting layer/electron-transporting layer” proposed by Tanget al. of Codak Eastman Co. This structure features a very highlight-emitting efficiency. Most of the light-emitting devices that havenow been studied and developed are employing this structure.

There may be further employed a structure in which the positivehole-injection layer/positive hole-transporting layer/light-emittinglayer/electron-transporting layer or positive hole-injectionlayer/positive hole-transporting layer/light-emittinglayer/electron-transporting layer/electron injection layer are laminatedon the anode in order mentioned. The light-emitting layer may be dopedwith a fluorescent pigment.

In this specification, the layers provided between the cathode and theanode are all called EL layers. Therefore, the above positivehole-injection layer, positive hole-transporting layer, light-emittinglayer, electron-transporting layer and electron injection layer allpertain to the EL layers.

A predetermined voltage is applied from a pair of electrodes to the ELlayer of the above structure, whereby the carriers are recombined in thelight-emitting layer to emit light. In this specification, alight-emitting element formed by the anode, EL layer and cathode iscalled EL element.

The EL layer possessed by the EL element is deteriorated by heat, light,moisture and oxygen. In fabricating the active matrix light-emittingdevice, therefore, the EL element is formed after the wiring and TFT areformed in the pixel portion.

After the EL element is formed, the substrate (EL panel) on which the ELelement is provided and a cover member are stuck and sealed (packaged)together with a sealing member in a manner that the EL element is notexposed to the external air.

After the air-tightness is heightened by the treatment such aspackaging, a connector (FPC, TAB, etc.) is attached for connecting theterminals drawn from the element or the circuit formed on the substrateto the external signal terminals, thereby to complete the active matrixlight-emitting device.

In the active matrix light-emitting device, however, a predeterminedvoltage (current flowing into the EL layer) applied to the EL layer fromthe pair of electrodes of the EL element is controlled by a transistorprovided in each of the pixels. Therefore, if some trouble occurs suchas failure of the function of the transistor in the pixel portion, breakor short-circuiting of the wiring, the predetermined voltage (current)is no longer applied to the EL layer possessed by the EL element. Insuch a case, the pixel no longer displays a desired gradation.

Even when the wiring or the transistor for controlling the emission oflight from the EL element is defective in the pixel portion, however, itis not possible to make sure the presence of the defect until thelight-emitting device is completed and is really used to make a display.In order to make a distinction from the acceptable products byinspection, therefore, the EL element must be completed though it mayinclude a pixel portion that does not serve as a completed product, thepackaging must be effected, and the connector must be attached tocomplete it as the light-emitting device. In this case, the step offorming the EL element, the step of packaging and the step of attachingthe connector are wasted, resulting in a loss of time and cost. Evenwhen the EL panel is formed by using a multi-chamfered substrate, thestep of packaging and the step of attaching the connector are wasted,similarly, resulting in the loss of time and cost.

In the active matrix liquid crystal displays that are mass-producedearlier than the active matrix light-emitting devices, it has been doneto form the wiring and TFT in the pixel portion prior to completing theliquid crystal display by introducing the liquid crystals into betweenthe two substrates, to electrically charge the capacitors possessed bythe pixels, and to measure the amount of electric charge for each of thepixels to make sure the presence of defects in the pixel portions.

In the active matrix light-emitting devices, however, not less than twoTFTs are generally included in each pixel. One electrode (pixelelectrode) and the capacitor in the EL element are often connectedtogether with the transistors sandwiched therebetween. In this case,measurement of the amount of electric charge stored in the capacitordoes not help make sure if the wiring and transistor connected betweenthe capacitor and the pixel electrode are defective. In the case of thelight-emitting device, further, an electric current must be supplied tothe EL element and, hence, it is necessary to measure the electriccurrent that flows.

It has been urged to establish the method of inspecting whether thewiring and transistor in the pixel portion are defective or, in otherwords, whether a predetermined voltage can be applied (or, whether apredetermined current can be supplied) to the pixel electrode of the ELelement of each pixel prior to completing the light-emitting device in aprocess toward mass-producing the active matrix light-emitting devices.

SUMMARY OF THE INVENTION

The inspection method utilizing electromagnetic waves disclosed in thisspecification inspects any defect in the semiconductor element formed onthe element substrate and in the pixels and wirings formed like a matrixwhich are connected to the semiconductor element.

In this specification, the element substrate refers to the one on whichthere are formed the pixel electrodes connected to the semiconductorelements among the pixels that are independently formed in the pixelportion after the wirings and the semiconductor elements have beenformed on the substrate. The semiconductor element stands for an elementwhich, by itself or in a plural number, constitutes a switching functionof a semiconductor material, as represented by a transistor and,particularly, by a field-effect transistor, typically MOS (metal oxidesemiconductor) transistor or a thin-film transistor (TFT). Accordingly,both the semiconductor substrate on which the MOS transistor is formedand the substrate on which the TFT is formed pertain to the elementsubstrates.

Among the wirings possessed by the pixel portion, the gate signal linesare successively selected to successively input the signals having thesame potential to the source signal lines in a state where all of thecurrent feed lines are maintained at the same potential, in order tosuccessively select all of the pixels. In this specification, the pixelthat is selected means that a video signal is Input to the source signalline possessed by the pixel in a state where the gate signal linepossessed by the pixel is selected.

Further, an opposing detector substrate is provided on the elementsubstrate, and electromagnetic waves (preferably, an X-rays) areradiated from an electromagnetic wave source 101 to a gas between theopposing detector substrate 102 and the element substrate 103 as shownin FIG. 1(A). The electromagnetic wave source is the one capable ofgenerating electromagnetic waves. When the electromagnetic waves aregenerated, a gas (air in this case) is ionized due to theelectromagnetic waves, whereby ions are generated and an electric pathis established along which a current flows. In this specification, theopposing detector substrate stands for the one on which is formed anelectrode through which a current flows into the pixel electrodepossessed by the pixel on the element substrate. The electrode formed onthe opposing detector substrate is called opposing detector electrode.Further, a current-flowing state stands for the one in which the currentflowing into the pixel electrode of the element substrate, flows intothe opposing detector electrode of the opposing detector substrate.

When a pixel is selected on the element substrate 103, the selectedpixel is connected to the opposing detector substrate 102. That is, uponsuccessively selecting the pixels on the element substrate, the pixelscan be electrically connected to the opposing detector substrate 102corresponding thereto. In detecting the current flowing into aparticular pixel on the element substrate as shown in FIG. 1(A), aposition at where the current flowing into the element substrate can bemore correctly measured, is called corresponding position. To providethe opposing detector substrate at a position corresponding to theelement substrate, the element substrate or the opposing detectorsubstrate must be so moved that the distance becomes the shortestbetween the pixel and the opposing detector electrode.

In this case, the current flowing into the opposing detector substrate102 can be measured by an ammeter 123 connected to the opposing detectorsubstrate 102. That is, the current measured here is due to the videosignal input to the selected pixel of the element substrate 103. Uponevaluating whether the measured current is lying within a predeterminedrange, it is allowed to inspect whether the wirings and the transistorspossessed by the pixels are defective.

When a pixel is selected and a current flowing into the pixel electrodeor into the electrically conducting film that serves as the pixelelectrode lies outside the predetermined range, it can be regarded thatthe transistor possessed by the pixel is not normally working or thewiring is broken or is short-circuited. On the other hand, when a pixelis selected and a current flowing into the pixel electrode or into theelectrically conducting film serving as the pixel electrode lies withinthe predetermined range, it can be regarded that the transistor and thewiring possessed by the pixel are normally working.

The range of current in which it can be regarded that the transistor andthe wiring are normally working, can be suitably set by a person whoconducts the inspection. When the number of the pixels in which thedefects are occurring (defective pixels) is not smaller than n in thepixel portion as a result of inspection, it is regarded that the elementsubstrate is defective. The number n of the defective pixels with whichthe device can be regarded to be defective, can be suitably set by theperson who conducts the inspection.

An organic compound layer is formed on the electrode (pixel electrode)that has been formed on the element substrate inspected by theinspection method of the invention and in contact thereto, and anelectrode (opposing electrode) is formed on the above organic compoundlayer in contact thereto to complete the light-emitting device. It isthen made possible to distinguish whether the element substrate isacceptable or defective without the need of really effecting thedisplay.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A–C are diagrams illustrating an inspection device of thisinvention;

FIGS. 2A–B are diagrams illustrating a pixel structure of the elementsubstrate and of the opposing detector substrate of this invention;

FIGS. 3(A) and 3(B) illustrate a method of evaluation relying upon theinspection according to this invention;

FIGS. 4(A) to 4(C) are diagrams illustrating how to fabricate alight-emitting device;

FIGS. 5(A) to 5(C) are diagrams illustrating how to fabricate thelight-emitting device;

FIGS. 6(A) to and 6(B) are diagrams illustrating how to fabricate thelight-emitting device;

FIG. 7(A) is a top view of an element substrate inspected according tothis invention;

FIG. 7(B) is a circuit diagram of the element substrate according tothis invention.

FIG. 8(A) is a top view of the opposing detector substrate used for theinvention;

FIG. 8(B) is a circuit diagram of the element substrate according tothis invention.

FIG. 9 is a diagram illustrating the inspection method of thisinvention;

FIG. 10 is a circuit diagram of pixels in the light-emitting device;

FIG. 11 is a diagram illustrating the constitution of the opposingdetector substrate of this invention;

FIG. 12 is a diagram illustrating the constitution of the opposingdetector substrate of this invention;

FIGS. 13A–F show electric appliances using the light-emitting device;

FIGS. 14A–C show electric appliances using the light emitting device;

FIG. 15 shows a light-emitting device inspected by the inspection methodof this invention; and

FIGS. 16(A) and 16(B) show light-emitting devices inspected by theinspection method of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inspection device and the method of inspecting the element substrateby using the inspection device according to the invention will now bedescribed with reference to FIG. 1. In this invention, the transistorused for the light-emitting device may be either a MOS transistor or athin-film transistor (hereinafter referred to as TFT). In the case ofthe TFT, further, there is no need of imposing limitation on thestructure, and there may be used a TFT of a structure such as of theplanar type or of the inverse stagger type. Further, the drive circuitfor the light-emitting device used in the invention may be a known one.

When the inspection method of the invention is used for thelight-emitting device having an EL element, the element structure of theEL element and the EL material may comply with those of known ones.

In this specification, the inspection device refers to the one includingthe source 101 of electromagnetic waves and the opposing detectorsubstrate 102 in combination. Here, however, the opposing detectorsubstrate 102 shown is an example of the invention, and is in no waylimited to the one of a shape shown in FIG. 1(A). The opposing detectorsubstrates of other shapes will be described in detail in the workingexamples in the specification.

The source 101 of electromagnetic waves is connected to a power source104. When a high voltage of several kilovolts is applied from the powersource 104 to two pieces of electrodes in the source 101 ofelectromagnetic waves, the electrons generated by the cathode impingeupon the anode to generate electromagnetic waves. In this invention, itis desired to use an X-ray or a soft X-ray having a wavelength of from0.01 to 100 nm. It is, however, also allowable to use electromagneticwaves that are capable of ionizing a gas existing between the opposingdetector substrate and the element substrate, if such electromagneticwaves are available.

The electromagnetic waves, in general, exhibit a photo-ionizationfunction. The principle is such that upon irradiating stable atoms andmolecules with electromagnetic waves, electrons in the atoms and in themolecules are sprung out, and the atoms and molecules assume thepositive (+) polarity since they are lacking electrons.

The electrons that are sprung out further attack other stable atoms andmolecules to generate atoms or molecules having the negative (−)polarity.

As a result, atoms and molecules that are ionized into the positivepolarity and the negative polarity are present in the gas irradiatedwith electromagnetic waves. In this invention, therefore, the elementsubstrate 103 and the opposing detector substrate 102 are overlapped asshown in FIG. 1(A) and are irradiated with electromagnetic waves fromthe source 101 of electromagnetic waves, so that the gas present betweenthe element substrate 103 and the opposing detector substrate 102 isirradiated with the electromagnetic waves. At this moment, the gas (air)is ionized with electromagnetic waves, and an electric passage of ionscan be formed between the element substrate 103 and the opposingdetector substrate 102. The gas referred to here is the air. It is,however, also allowable to use a gas that is subject to be more ionized.It is further desired that the distance between the opposing detectorsubstrate 102 and the element substrate 103 is as close as possible.Concretely speaking, it is desired that the distance between theopposing detector substrate 102 and the element substrate 103 is notlarger than 500 μm.

On the element substrate 103 are formed plural pixels in the form of amatrix. Further, the element substrate 103 is connected to the drivecircuit (A) 107. The drive circuit (A) 107 includes a drive circuit ofthe gate side and a drive circuit of the source side. As shown in FIG.1(A), for example, a pixel 105 is selected when a selection signal isinput to the pixel 105 from the drive circuit of the gate side. Theselection signal referred to here stands for a signal that opens thegate electrode when a signal is input to the gate electrode connected tothe gate line. A state where the gate electrode possessed by the pixelis opened by the selection signal is referred to as that the pixel isselected. When the pixel 105 is selected and a video signal is inputthereto from the drive circuit of the source side, a current flows intothe pixel electrode of the pixel 105 on the element substrate 103. Thecurrent further flows into opposing portions 106 formed on the opposingdetector substrate 102 passing through the gas ionized byelectromagnetic waves. In this specification, the opposing portions 106are the ones formed like a matrix on the opposing detector substrate 102being corresponded to the pixels 105 formed on the element substrate103. On each opposing portion, there are formed an opposing detectorelectrode into which a current flows from the element substrate 103 andan inspection TFT 120 connected to the opposing detector electrode. Inthis specification, the inspection TFT 120 stands for a TFT which iscapable of flowing a current from the selected pixel electrode on theelement substrate 103 through the opposing detector electrode when thegate electrode is opened by a selection signal input from a drivecircuit (B) 108 connected to the opposing detector substrate 102.

FIG. 1(B) is a diagram illustrating, on an enlarged scale, the pixels105 formed like a matrix on the element substrate 103. Here, though theTFT is exemplified as a transistor, it is also allowable to use a MOStransistor. Referring to FIG. 1(B), the element substrate 103 foreffecting the inspection includes a drive TFT formed on an insulator andTFTs (switching TFT and current control TFT) in the pixel portion.

In FIG. 1(B), reference numeral 110 denotes a switching TFT. The gateelectrode of the switching TFT 110 is connected to a gate signal line111. The source region and drain region of the switching TFT 110 are soconnected that either one of them is connected to the source signal line112 and the other one is connected to the gate electrode of the currentcontrol TFT 113 and to a capacitor 114 possessed by the pixels.

The capacitor 114 is for holding a gate voltage of the current controlTFT 113 (potential difference between the gate electrode and the sourceregion) when the switching TFT 110 has not been selected (off-state).Though the capacitor 114 is provided, here, the invention is in no waylimited to the above constitution only, and the capacitor 114 may not beprovided.

Further, the source region and drain region of the current control TFT113 are so connected that either one of them is connected to a currentfeeder line 115 and the other one is connected to the pixel electrodepossessed by the pixel 105. When an electric passage is formed by theirradiation with electromagnetic waves, the pixel electrode is connectedto the source region of an inspection TFT (120 in FIG. 1(C)) possessedby the opposing portion 106 on the opposing detector substrate 102. Thecurrent feeder line 115 is connected to the capacitor 114.

FIG. 1(C) is a diagram illustrating, on an enlarged scale, the opposingportions 106 formed like a matrix on the opposing detector substrate102. An inspection TFT 120 is formed on each opposing portion, and thegate electrode is connected to a gate signal line 121 connected to thedrive circuit (B) 108. When a pixel on the element substrate 103 isselected, an opposing portion 106 corresponding to the selected pixel onthe substrate is selected by a selection signal from the drive circuit(B) 108. The drain region of the inspection TFT 120 is connected to adrain wiring 122 which is connected to an ammeter 123 on the externalside.

The current feeder line 122 is served with a power source potentialwhich is produced by a power source constituted by an external IC.

The switching TFT 110 and the current control TFT 113 may be either ofthe n-channel type or the p-channel type. When the source region or thedrain region of the current control TFT 113 is connected to the anode ofan EL element that is formed later, however, it is desired that thecurrent control TFT 113 is of the p-channel type. When the source regionor the drain region of the current control TFT 113 is connected to thecathode of the EL element, further, it is desired that the currentcontrol TFT 113 is of the n-channel type.

Further, the switching TFT 110 and the current control TFT 113 may be ofa multi-gate structure such as the double-gate structure or thetriple-gate structure in addition to the single-gate structure.

Next, FIGS. 2(A) and 2(B) illustrate the opposing detector substrate 102of the invention and the element substrate 103 to be inspected thereby.A pixel portion 201 shown in FIG. 2(A) is the one on which the pixels105 shown in FIG. 1(B) are formed like a matrix. The pixel portion 201of FIG. 2(A) is provided with source signal lines (S1 to Sx), currentfeeder lines (V1 to Vx) and gate signal lines (G1 to Gy).

Here, the pixel 105 is a region including source signal line (S1 to Sx),current feeder line (V1 to Vx) and gate signal line (G1 to Gy) each in anumber of one.

FIG. 2(B) illustrates the opposing portions 106 formed like a matrix onthe opposing detector substrate 102 according to the invention. FIG.2(B) shows gate signal lines (G1 to Gx). The opposing portions 106 areselected by signals from the gate signal lines (G1 to Gx). The drainregion of the inspecting TFT 120 in each opposing portion 106 isconnected to the current line (A) and is connected to an externalammeter 123.

That is, a current flows from a selected pixel on the element substrate103 through an electric passage into a selected opposing portion 106 onthe opposing detector substrate 102, and is detected by the ammeter 123.Either one or both of a stage securing the opposing detector substrateand a stage securing the element substrate may be provided with apositioning function, so that the distance becomes as small as possiblebetween the pixel 105 on the element substrate 103 and the correspondingopposing portion 106 on the opposing detector substrate 102.

Next, described below with reference to FIG. 3 is a method of evaluatingthe switching TFTs 110 and current control TFTs 113 in the pixels 105 onthe element substrate 103 by using the inspection method of theinvention.

FIG. 3(A) shows the pixels formed in the pixel portion 201 on theelement substrate 103 by way of X-Y coordinates (X, Y). Here, pixels ofX columns are formed on the surface of the paper in the transversedirection, and pixels of Y rows are formed on the surface of the paperin the longitudinal direction.

When the gate electrode of the pixel is selected, a video signal isinput to the selected pixel from the source signal line electricallyconnected to the source signal line drive circuit. At this moment, thecurrent flows into the pixel electrode, input to the inspection TFT 120from the opposing detector electrode of the opposing detector substrate102 through the electric passage formed in the gas by the irradiationwith the electromagnetic waves and is, further, input to the ammeter 123connected on the external side passing through the drain wiring. Here,the current flowing between the selected pixel on the element substrate103 and the corresponding opposing portion is measured by the ammeter123. It is further allowable to form the ammeter 123 on the opposingdetector substrate 102.

In this embodiment, when the video signal contains “white” datairrespective of whether it may be in an analog form or in a digitalform, the current control TFT 113 is turned on. Therefore, the powersource potential is applied to the pixel electrode. As a result, acurrent flows from the pixel that has received the video signalcontaining “white” data to the opposing portion 106 on the opposingdetector substrate 102 and to the ammeter 123.

Conversely, when the video signal contains “black” data, the currentcontrol TFT 113 formed on the element substrate 103 is turned off.Therefore, the power source potential is not applied to the pixelelectrode. As a result, a current flows from the pixel that has receivedthe video signal containing “black” data to the opposing portion 106 onthe opposing detector substrate 102 and to the ammeter 123, the currentbeing smaller than the current of when a video signal containing “white”data is input.

In the foregoing was described the case where both the switching TFT 110and the current control TFT 113 are normally working. When either one ofthem is defective, however, it happens that a current that should flowfails to flow or a current that should not flow flows.

In this invention, therefore, a current of when the video signal is“black” and a current of when the video signal is “white” are measuredin advance by using a pixel having a TFT that normally works to use themas reference data.

In this invention, further, the data are evaluated by using a ratio ofcurrents (ratio of white and black) that flow when the video signals arewhite and black, respectively.

FIG. 3(B) illustrates the measured results represented by a ratio ofstandardized (normalized) white and black signals. In thisstandardization (normalization), 100 represents a sufficiently largeratio (contrast) of black and white by using the reference data. In thistable, the ordinate represents the ratio of white and black, and theabscissa represents the coordinate of pixels. Further, a reference isset for the ratio of white and black, and the device is regarded to beacceptable when the ratio of white and black is not smaller than 20 butis not larger than 100. That is, the hatched region of FIG. 3(B)represents references of acceptable devices.

However, when the ratio of white and black is lower than the referencevalue like a coordinate (1, 3), the device is judged to be defective andis removed from the subsequent steps. The acceptable reference for theratio of white and black may be set depending upon a level that isrequired.

Upon evaluating the characteristics of the pixels relying upon the abovemethod, the defective products can be discovered at an early time.Accordingly, the defective products are removed from the subsequentproduction process such as formation of EL element. Depending upon thedegree of defect, further, the device may be repaired through a step ofrepairing and may be returned back to the subsequent steps. Describedbelow in detail in the following examples is a method of completing thelight-emitting device by forming an organic compound layer and a cathode(second electrode) on the pixel electrode (first electrode) after thestep of inspecting the element substrate has been finished.

This makes it possible to decrease the loss that results when thedefective product is passed through up to the final step and to improvethe yield owing to the repairing.

EXAMPLE 1

A method of manufacturing a pixel TFT and TFTs of a driver circuit(source signal line driver circuit, gate signal line driver circuit andpixel selective signal line driver circuit) provided in the periphery ofa pixel portion is explained in this embodiment. For simplicity of theexplanation, the CMOS circuit which is a basic unit concerning with thedriver circuit is illustrated.

First, as shown in FIG. 4A, a base film 5002 made of an insulating filmsuch as a silicon oxide film, a silicon nitride film, or a siliconoxynitride film is formed on a substrate 5001 made from glass, such asbarium borosilicate glass or aluminum borosilicate glass, typicallyCorning Corp. #7059 glass or #1737 glass. For example, a siliconoxynitride film 5002 a manufactured from SiH₄, NH₃, and N₂O by plasmaCVD is formed with a thickness of 10 to 200 nm (preferably from 50 to100 nm), and a hydrogenized silicon oxynitride film 5002 b with athickness of 50 to 200 nm (preferably between 100 and 150 nm),manufactured from SiH₄ and N₂O, is similarly formed and laminated. Thebase film 5002 with the two layer structure is shown in Embodiment 1,but the base film 5002 may also be formed as a single film or as alamination film in which two or more layers are laminated.

Island shape semiconductor layers 5003 to 5006 are formed of crystallinesemiconductor film manufactured by using a laser crystalline method or aknown thermal crystallization method with a semiconductor film having anamorphous structure. The thickness of the island shape semiconductorlayers 5003 to 5006 is set from 25 to 80 nm (preferably between 30 and60 nm). There are no limitations on the crystalline semiconductor filmmaterial, but it is preferable to form the film from a semiconductormaterial such as silicon or a silicon germanium (SiGe) alloy.

A laser such as a pulse oscillation type or continuous emission typeexcimer laser, a YAG laser, or a YVO₄ laser can be used as a laser lightsource in manufacturing the crystalline semiconductor film with thelaser crystallization method. A method of condensing laser light emittedfrom a laser oscillator into a linear shape by an optical system andthen irradiating the light to the semiconductor film may be employedwhen these types of lasers are used. The crystallization conditions maybe suitably selected by the operator. However, the pulse oscillationfrequency is set to 300 Hz, and the laser energy density is set from 100to 400 mJ/cm² (typically between 200 and 300 mJ/cm²) when using theexcimer laser. Further, the second harmonic is utilized when using theYAG laser, the pulse oscillation frequency is set from 30 to 300 Hz, andthe laser energy density may be set from 300 to 600 mJ/cm² (typicallybetween 350 and 500 mJ/cm²). The laser light which has been condensedinto a linear shape with a width of 100 to 1000 mm, for example 400 mm,is then irradiated onto the entire surface of the substrate. This isperformed with an overlap ratio of 50 to 90% for the linear laser light.

A gate insulating film 5007 is formed covering the island shapesemiconductor layers 5003 to 5006. The gate insulating film 5007 isformed of an insulating film containing silicon having a thickness of 40to 150 nm by plasma CVD or sputtering. A 120 nm thick silicon oxynitridefilm is formed in Embodiment 1. The gate insulating film is not limitedto this type of silicon oxynitride film, of course, and other insulatingfilms containing silicon may also be used, in a single layer or in alamination structure. For example, when using a silicon oxide film, itcan be formed by plasma CVD with a mixture of TEOS (tetraethylorthosilicate) and O₂, at a reaction pressure of 40 Pa, with thesubstrate temperature set from 300 to 400° C., and by discharging at ahigh frequency (13.56 MHZ) electric power density of 0.5 to 0.8 W/cm².Good characteristics as a gate insulating film can be obtained bysubsequently performing thermal annealing, at between 400 and 500° C.,of the silicon oxide film thus manufactured.

A first conductive film 5008 and a second conductive film 5009 are thenformed on the gate insulating film 5007 in order to form gateelectrodes. The first conductive film 5008 is formed from Ta with athickness of 50 to 100 nm, and the second conductive film 5009 is formedby W with a thickness of 100 to 300 nm, in Embodiment 1.

The Ta film is formed by sputtering, and sputtering with a Ta target isperformed by using Ar. If appropriate amounts of Xe and Kr are added tothe Ar during sputtering, the internal stress of the Ta film will berelaxed, and film peeling can be prevented. The resistivity of α phaseTa film is on the order of 20 μΩcm, and it can be used in the gateelectrode, but the resistivity of β phase Ta film is on the order of 180μΩcm and it is unsuitable for the gate electrode. The α phase Ta filmcan easily be obtained if a tantalum nitride film, which possesses acrystal structure near that of α phase Ta, is formed with a thickness of10 to 50 nm as a base for Ta in order to form the α phase Ta film.

A W film is formed by sputtering with a W target. The W film can also beformed by thermal CVD using tungsten hexafluoride (WF₆). Whichever isused, it is necessary to make the film become low resistance in order touse it as the gate electrode, and it is preferable that the resistivityof the W film be made equal to or less than 20 μΩcm. The resistivity canbe lowered by enlarging the crystals of the W film, but for cases inwhich there are many impurity elements such as oxygen within the W film,crystallization is inhibited, and the film becomes high resistance. A Wtarget having a purity of 99.9999% is thus used in sputtering. Inaddition, the W film is formed while sufficient care is taken in orderthat no impurities From within the gas phase are introduced at the timeof film formation. Thus, a resistivity of 9 to 20 μΩcm can be achieved.

Note that, although the first conductive film 5008 is Ta and the secondconductive film 5009 is W in Embodiment 1, the conductive films are notlimited to these. Both the first conductive film 5008 and the secondconductive film 5009 may also be formed from an element selected fromthe group consisting of Ta, W, Ti, Mo, Al, and Cu, from an alloymaterial having one of these elements as its main constituent, or from achemical compound of these elements. Further, a semiconductor film,typically a polysilicon film, into which an impurity element such asphosphorous is doped may also be used. Examples of preferablecombinations other than that used in Embodiment 1 include: a combinationof the first conductive film 5008 formed from tantalum nitride (TaN) andthe second conductive film 5009 formed from W; a combination of thefirst conductive film formed from tantalum nitride (TaN) and the secondconductive film 5009 formed from Al; and a combination of the firstconductive film 5008 formed from tantalumnitride (TaN) and the secondconductive film 5009 formed from Cu.

A mask 5010 is formed next from resist, and a first etching process isperformed in order to form electrodes and wirings. An ICP (inductivelycoupled plasma) etching method is used in Embodiment 1. A gas mixture ofCF₄ and Cl₂ is used as an etching gas, and a plasma is generated byapplying a 500 W RF electric power (13.56 MHZ) to a coil shape electrodeat 1 Pa. A 100 W RF electric power (13.56 MHZ) is also applied to thesubstrate side (test piece stage), effectively applying a negativeself-bias. The W film and the Ta film are both etched on the same orderwhen CF₄ and Cl₂ are combined.

Edge portions of the first conducting layer and the second conductinglayer are made into a tapered shape in accordance with the effect of thebias voltage applied to the substrate side with the above etchingconditions by using a suitable resist mask shape. The angle of thetapered portions is from 15 to 45°. The etching time may be increased byapproximately 10 to 20% in order to perform etching without any residueremaining on the gate insulating film. The selectivity of a siliconoxynitride film with respect to a W film is from 2 to 4 (typically 3),and therefore approximately 20 to 50 nm of the exposed surface of thesilicon oxynitride film is etched by this over-etching process. Firstshape conductive layers 5011 to 5016 (first conductive layers 5011 a to5016 a and second conductive layers 5011 b to 5016 b) composed of thefirst conducting layer and the second conducting layer are thus formedby the first etching process. Portions of the gate insulating film 5007not covered by the first shape conductive layers 5011 to 5016 are etchedon the order of 20 to 50 nm, forming thinner regions. (See FIG. 4A.)

A first doping process is then performed, and an impurity element whichimparts n-type conductivity is added. Ion doping or ion injection may beperformed as the doping method. Ion doping is performed at conditions inwhich the dosage is set to 1×10¹³ to 5×10¹⁴ atoms/cm², and anacceleration voltage is set between 60 and 100 keV. An element residingin group 15 of the periodic table, typically phosphorous (P) or arsenic(As), is used as the n-type conductivity imparting impurity element.Phosphorous (P) is used here. The conductive layers 5011 to 5015 becomemasks with respect to the n-type conductivity imparting impurityelement, and first impurity regions 5017 to 5025 are formed in aself-aligning manner. The impurity element which imparts n-typeconductivity is added to the first impurity regions 5017 to 5025 at aconcentration within a range of 1×10²⁰ and 1×10²¹ atoms/cm³. (See FIG.4B.)

A second etching process is performed without removing resist mask nextas shown in FIG. 4C. The W film is etched selectively using a mixture ofCF₄, Cl₂, and O₂ is used as the etching gas. At that time, by the secondetching process, second shape conductive layers 5026 to 5031 (firstconductive layers 5026 a to 5031 a and second conductive layers 5026 bto 5031 b) are formed. The gate insulating film 5007 is additionallyetched on the order of 20 to 50 nm, forming thinner regions, in regionsnot covered by the second shape conductive layers 5026 to 5031.

The etching reaction of the W film or the Ta film in accordance with themixed gas of CF₄ and Cl₂ can be estimated from the generated radicals,or from the ion types and vapor pressures of the reaction products.Comparing the vapor pressures of W and Ta fluorides and chlorides, the Wfluoride compound WF₆ is extremely high, and the vapor pressures ofWCl₅, TaF₅, and TaCl₅ are of similar order. Therefore the W film and theTa film are both etched by the CF₄ and Cl₂ gas mixture. However, if asuitable quantity of O₂ is added to this gas mixture, CF₄ and O₂ react,forming CO and F, and a large amount of F radicals or F ions aregenerated. As a result, the etching speed of the W film having a highfluoride vapor pressure becomes high. On the other hand, even if Fincreases, the etching speed of Ta does not relatively increase.Further, Ta is easily oxidized compared to W, and therefore the surfaceof Ta is oxidized by the addition of O₂. The etching speed of the Tafilm is further reduced because Ta oxides do not react with fluorine andchlorine. It therefore becomes possible to have a difference in etchingspeeds of the W film and the Ta film, and it becomes possible to makethe etching speed of the W film larger than that of the Ta film.

A second doping process is then performed as shown in FIG. 5A. In thiscase, an impurity element which imparts n-type conductivity is dopedunder conditions of a lower dosage than that in the first dopingprocess, and at a higher acceleration voltage than that in the firstdoping process. For example, doping may be performed at an accelerationvoltage of 70 to 120 keV and with a dosage of 1×10¹³ atoms/cm², formingnew impurity regions inside the first impurity regions formed in theisland shape semiconductor layers of FIG. 4B. Doping is performed withthe first shape conductive layers 5026 to 5030 as masks with respect tothe impurity element, and doping is done such that the impurity elementis also added to regions below the first conductive layers 5026 a to5030 a. Third impurity regions 5032 to 5036 are formed. A concentrationof phosphorus (P) added to the third impurity region 5032 to 5036 isprovided with a gradual concentration gradient in accordance with a filmthickness of the taper portion of the first conductive layer 5026 a to5030 a. Further, in the semiconductor layer overlapping the taperportion of the first conductive layer 5026 a to 5030 a, from an endportion of the taper portion of the first conductive layer 5026 a to5030 a toward an inner side, the impurity concentration is more or lessreduced, however, the concentration stays to be substantially the samedegree.

As shown in FIG. 5B, a third etching process is performed. This isperformed by using a reactive ion etching method (RIE method) with anetching gas of CHF₆. The tapered portions of the first conductive layers5026 a to 5031 a are partially etched, and the region in which the firstconductive layers overlap with the semiconductor layer is reduced by thethird etching process. Third shape conductive layers 5037 to 5042 (firstconductive layers 5037 a to 5042 a and second conductive layers 5037 bto 5042 b) are formed. At this point, regions of the gate insulatingfilm 5007, which are not covered with the third shape conductive layers5037 to 5042 are made thinner by about 20 to 50 nm by etching.

By the third etching process, third impurity regions 5032 a to 5036 a,which overlap with the first conductive layers 5037 a to 5041 a, andsecond impurity regions 5032 b to 5236 b between the first impurityregions and the third impurity regions are formed in the third impurityregions.

Then, as shown in FIG. 5C, the third doping process is performed to formthe fourth impurity regions 5043 to 5054, which have a conductivity typeopposite to the first conductivity type, in the island-likesemiconductor layers 5004, 5006 forming p-channel TFTs. The thirdconductive layers 5038 b to 5041 b are used as masks to an impurityelement, and the impurity regions are formed in a self-aligning manner.At this time, the whole surfaces of the island-like semiconductor layers5003, 5005 and the wiring portion 5042, which form n-channel TFTs arecovered with a resist mask 5200. Phosphorus is added to the impurityregions 5043 to 5054 at different concentrations, respectively. Theregions are formed by an ion doping method using diborane (B₂H₆) and theimpurity concentration is made 2×10²⁰ to 2×10²¹ atoms/cm³ in any of theregions.

By the steps up to this, the impurity regions are formed in therespective island-like semiconductor layers. The third shape conductivelayers 5043 to 5054 overlapping with the island-like semiconductorlayers function as gate electrodes. The conductive layer 5042 functionsas an island-like source signal line.

After the resist mask 5200 is removed, a step of activating the impurityelements added in the respective island-like semiconductor layers forthe purpose of controlling the conductivity type is conducted. This stepis carried out by a thermal annealing method using a furnace annealingoven. In addition, a laser annealing method or a rapid thermal annealingmethod (RTA method) can be applied. The thermal annealing method isperformed in a nitrogen atmosphere having an oxygen concentration of 1ppm or less, preferably 0.1 ppm or less and at 400 to 700° C., typically500 to 600° C. In Embodiment 1, a heat treatment is conducted at 500° C.for 4 hours. However, in the case where a wiring material used for thethird conductive layers 5037 to 5042 is weak to heat, it is preferablethat the activation is performed after an interlayer insulating film(containing silicon as its main ingredient) is formed to protect thewiring line or the like.

Further, a heat treatment at 300 to 450° C. for 1 to 12 hours isconducted in an atmosphere containing hydrogen of 3 to 100%, and a stepof hydrogenating the island-like semiconductor layers is conducted. Thisstep is a step of terminating dangling bonds in the semiconductor layerby thermally excited hydrogen. As another means for hydrogenation,plasma hydrogenation (using hydrogen excited by plasma) may be carriedout.

Next, as shown in FIG. 6A, a first interlayer insulating film 5055 madeof an inorganic insulator material is formed. In this embodiment, afirst interlayer insulating film 5055 made of a silicon nitride filmhaving a thickness of 100 to 200 nm is formed. A second interlayerinsulating film 5056 made of an organic insulator material formedthereon. Contact holes are then formed with respect to the firstinterlayer insulating film 5055, the second interlayer insulating film5056, and the gate insulating film 5007, respective wirings (includingconnection wirings and signal lines) 5057 to 5062, and 5064 are formedby patterning, and then, a pixel electrode 5063 that contacts with theconnection wiring 5062 is formed by patterning.

Next, the film made from organic resin is used for the second interlayerinsulating film 5056. As the organic resin, polyimide, polyamide, acryl,BCB (benzocyclobutene) or the like can be used. Especially, since thesecond interlayer insulating film 5056 has rather the meaning offlattening, acryl excellent in flatness is desirable. In Embodiment 1,an acryl film is formed to such a thickness that stepped portions formedby the TFTs can be adequately flattened. The thickness is preferablymade 1 to 5 μm (more preferably 2 to 4 μm).

In the formation of the contact holes, dry etching or wet etching isused, and contact holes reaching the n-type impurity regions 5017, 5018,5021 and 5023 or the p-type impurity regions 5043 to 5054, a contacthole reaching the wiring 5042, a contact hole reaching the power sourcesupply line (not shown), and contact holes reaching the gate electrodes(not shown) are formed, respectively.

Further, a lamination film of a three layer structure, in which a 100 nmthick Ti film, a 300 nm thick aluminum film containing Ti, and a 150 nmthick Ti film are formed in succession by sputtering, is patterned intoa desirable shape, and the resultant lamination film is used as thewirings (including connection wirings and signal lines) 5057 to 5062,and 5064. Of course, other conductive films may be used.

In this example, further, an ITO film is formed maintaining a thicknessof 110 [nm] as a pixel electrode 5063 and is patterned. The pixelelectrode 5063 is overlapped on the connection wiring 5062 in contacttherewith. It is also allowable to use a transparent electricallyconducting film by mixing 2 to 20 [%] of zinc oxide (ZnO) into indiumoxide. The pixel electrode 5063 serves as an anode of the EL element(FIG. 6(A)). When the area of the wiring region increases relative tothe area of the pixel electrode, error increases due to a relation ofdetection. It is therefore desired that the ratio of pixel area islarge. Besides, the display element requires a high numerical aperture,and the requirements of the two are in agreement.

After formed up to this point, the element substrate is inspected byusing the inspection method and the inspection device of the inventionas described in the Example of the invention. FIG. 7(A) is a top viewand FIG. 7(B) is a circuit diagram of the pixel portion of thelight-emitting device formed up to this point according to the Example.Common reference numerals are used in FIGS. 7(A) and 7(B).

The source of a switching TFT 702 is connected to a source wiring 715,and the drain region is connected to a drain wiring 705. The drainwiring 705 is electrically connected to a gate electrode 707 of acurrent control TFT 706. Further, the source of the current control TFT706 is electrically connected to a current feeder line 716, and thedrain region is electrically connected to a drain wiring 717. The drainwiring 717 is further electrically connected to a pixel electrode(anode) 718 indicated by a dotted line.

Here, a holding capacity is formed in a region designated at 719. Theholding capacity 719 is formed among a semiconductor film 720electrically connected to the current feeder line 716, an insulatingfilm (not shown) of the same layer as the gate-insulating film and thegate electrode 707. It is also possible to use, as a holding capacity,the capacity formed by the gate electrode 707, a layer (not shown) sameas the first interlayer-insulating film and the current feeder line 716.

FIG. 8 is a top view of the opposing detector substrate used in theExample. The opposing detector substrate in this Example may use a glassor quartz as a material that permits electromagnetic waves to easilypass through. Further, this Example uses a soft X-ray of electromagneticwaves of wavelengths of from 0.1 to 100 nm. The opposing detectorsubstrate can be fabricated by using the same method as the one forfabricating the element substrate described in Example. Here, however,the opposing detector electrode formed on the opposing detectorsubstrate is formed of beryllium or aluminum which is different from thematerial forming the pixel electrodes of the element substrate, andshould permit soft X-rays to easily pass through. These materials may beformed on the whole surface of the opposing portions, or may be formedlike stripes or like a mesh.

When the opposing detector substrate is formed by anotherlow-temperature film-forming process, there can be used an organic resinsuch as vinyl chloride or acrylic resin in addition to glass and quartz.

Reference numeral 801 denotes an inspection TFT. The source region 802of the inspection TFT 801 is connected to the opposing detectorelectrode through a source wiring 803, and is electrically connected tothe pixel electrode of the element substrate when the gas in the air isirradiated with the soft X-rays to form an electric passage. Further,the drain region 804 of the inspection TFT 801 is connected to the drainwirings (805 a and 805 b), and is electrically connected to an ammeter(not shown) provided on the outer side.

The gas is ionized upon being irradiated with the soft X-rays. In thisinvention, the ionization stands for the one that is ionized to such anextent that a current flows from the pixel electrode to the opposingdetector electrode through the ionized gas.

The gate electrode 806 is connected to the gate line 807, and theopposing detector electrode is a region indicated by a dotted line 808.

The element substrate having the pixel electrode is formed and is, then,inspected in a manner as described below. First, the element substrate901 and the opposing detector substrate 902 are arranged up and down asshown in FIG. 9 to carry out the inspection. In this embodiment, theelement substrate 901 and the opposing detector substrate 902 arearranged in a manner as shown in FIG. 9, and the electromagnetic wavesare radiated from the upper side of the opposing detector substrate toionize the air. The invention, however, is in no way limited theretoonly but may be such that the air is ionized to form an electric passageto flow an electric current between the element substrate 901 and theopposing detector substrate 902.

When the opposing detector substrate 902 is irradiated with the softX-rays from the source 903 of electromagnetic waves, the soft X-rayspass through the opposing detector substrate 902, and the air betweenthe opposing detector substrate 902 and the element substrate 901 isirradiated with the soft X-rays. In FIG. 9, the air is ionized by thesoft X-rays, and there is formed an apparent resistance as designated at907.

Thus, an electric passage is formed in the air. When a video signal isinput to the selected pixel on the element substrate 901, therefore, acurrent flowing into the pixel electrode 904 also flows into theopposing detector electrode 905 on the opposing detector substrate 902passing through the electric passage.

The current, then, flows into an external ammeter 906 through the drainwiring from the source region of the inspecting TFT connected to theopposing detector electrode 905 via the drain region. Currents flowinginto the pixel electrode are detected by the external ammeter at thetime when the video signal is input (white) to the pixel on the elementsubstrate 901 and when no video signal is input thereto (black), and areexpressed as a ratio of white and black to evaluate the quality of TFTon the element substrate 901. The process for forming the EL element isconducted while removing those devices of qualities lower than areference value. Depending upon the cause of defect and the degree ofdefect, further, the devices may be repaired through a repairing stepand may be returned back to the subsequent steps.

Referring next to FIG. 6(B), the insulating film containing silicon(silicon oxide film in this embodiment) is formed maintaining athickness of 500 [nm], an opening is formed at a position correspondingto the pixel electrode 5063, and a third interlayer-insulating film 5065is formed to serve as a bank. The opening is formed by the wet etchingmethod thereby to easily form the tapered side walls. Attention must begiven to that unless the side walls of the opening portion are formedsufficiently mildly, the EL layer is deteriorated to a conspicuousdegree due to a step.

Next, the EL layer 5066 and the cathode (MgAg electrode) 5067 arecontinuously formed by the, vacuum evaporation method without beingexposed to the open air. Here, the EL layer 5066 should have a thicknessof 80 to 200 [nm](typically, 100 to 120 [nm]) and the cathode 5067should have a thickness of 180 to 300 [nm](typically, 200 to 250 [nm]).

At this step, there are successively formed the EL layer 5066 and thecathode 5067 for the pixel corresponding to red color, for the pixelcorresponding to green color and for the pixel corresponding to bluecolor. Here, however, the EL layer 5066 has a poor resistance againstthe solution and must be separately formed for each of the colorswithout relying upon the photolithography technology. It is thereforedesired to employ a method such as evaporation method of selectivelyforming the EL layer 5066 and the cathode 5067 on the required portionsonly while concealing the areas except the desired pixels by using ametal mask.

First, a mask is set to conceal all areas except the pixelscorresponding to red color, and the EL layer 5066 that emits red lightis selectively formed by using the mask. Next, a mask is set to concealall areas except the pixels corresponding to green color, and the ELlayer that emits green light is selectively formed by using the mask.Then, a mask is set to conceal all areas except the pixels correspondingto blue color, and the EL layer that emits blue light is selectivelyformed by using the mask. Though different masks were used above, it isalso allowable to use the same mask.

Though in the foregoing was used the system for forming EL elements ofthree kinds corresponding to RGB, there may be used a system combining awhite light-emitting EL element and a color filter, a system combining ablue light-emitting or green light-emitting EL element and a fluorescentmaterial (fluorescent color conversion layer: CCM) or a system using atransparent electrode as the cathode (opposing electrode) andoverlapping thereon EL elements corresponding to RGB.

Known materials can be used for forming the EL layer 5066. As the knownmaterial, there can be preferably used an organic material by taking thedrive voltage into consideration. For example, four layers comprising apositive hole-injection layer, a positive hole-transporting layer, alight-emitting layer and an electron injection layer may be used as theEL layer.

Next, an opposing electrode 5067 is formed by using a metal mask on thepixels (pixels of the same line) having switching TFTs of which the gateelectrodes are connected to the same gate signal line. Though MgAg whichis a cathode material was used for the opposing electrode 5067 in thisExample, it should be noted that the invention is not limited theretoonly, but any other known material may be used as the opposing electrode5067.

Finally, a passivation film 5068 which is a silicon nitride film isformed maintaining a thickness of 300 [nm]. Upon forming the passivationfilm 5068, the EL layer 5066 is protected from the moisture so as toexhibit further improved reliability of EL elements.

Thus, the light-emitting device of a structure shown in FIG. 6(B) iscompleted. In the step of forming the light-emitting device according tothis Example, the source signal lines are formed by using Ta and W whichare the materials forming the gate electrodes, and the gate signal linesare formed by using Al which is a wiring material forming the drainelectrodes due to the circuit constitution and the steps. It is,however, allowable to use different materials, too.

Upon arranging TFTs of an optimum structure not only in the pixelportion but also in the drive circuit portion, the light-emitting deviceof this Example exhibits a very high reliability and improved operationcharacteristics. In the step of crystallization, further, it is alsoallowable to add a metal catalyst such as Ni to enhance thecrystallinity. This enables the source signal line drive circuit tooperate at a drive frequency of not lower than 10 [MHz].

First, in order to prevent the drop in the operation speed as much aspossible, the TFT of a structure which suppresses the injection of hotcarriers is used as the n-channel TFT for the CMOS circuit that formsthe drive circuit portion. The drive circuit referred to here includesshift registers, buffers, and level shifters, and includes latches inthe line sequential drive and includes transmission gates in the pointsequential drive.

In the case of this Example, the active layer of the n-channel TFTincludes the source region, drain region, overlapped LDD region (L_(OV)region) overlapped on the gate electrode with the gate-insulating filmsandwiched therebetween, an offset LDD region (L_(OFF) region) which isnot overlapped on the gate electrode with the gate-insulating filmsandwiched therebetween, and channel-forming region.

The p-channel TFT of the CMOS circuit needs not be particularly providedwith the LDD region since it is not almost deteriorated by the injectionof hot carriers. It is, of course, allowable to provide the LDD regionlike the N-channel TFT to cope with the hot carriers.

Further, when the drive circuit employs the CMOS circuit in which thecurrent flows in both directions through the channel-forming region,i.e., employs the CMOS circuit in which the roles of the source regionand of the drain region are replaced by each other, it is desired thatthe n-channel TFT forming the CMOS circuit forms the LDD regions on bothsides of the channel-forming region in such a manner that the LDDregions sandwich the channel-forming region. Such an example can berepresented by a transmission gate used for the point sequential drive.Further, when the drive circuit employs the CMOS circuit which mustsuppress the off current as small as possible, it is desired that then-channel TFT forming the CMOS circuit has the L_(OV) region. This canalso be exemplified by the transmission gate used for the pointsequential drive.

In practice, further, when the device is completed up to the state ofFIG. 6(B), it is desired to package (seal) the device with a protectionfilm (laminate film, etc.) having high air-tightness permitting the gasto escape little or with a light-transmitting sealing member so that thedevice will not be exposed to the open air. In this case, the interiorof the sealing member may be filled with an inert atmosphere or ahygroscopic material (e.g., barium oxide) may be arranged therein toimprove the reliability of the EL element.

After the air-tightness is enhanced by the treatment such as packaging,the device is completed as the product by attaching a connector(flexible printed circuit: FPC) for connecting the element formed on thesubstrate or for connecting the terminals drawn from the circuit to theexternal signal terminals. The device in a state that can be shipped iscalled light-emitting device in this specification.

EXAMPLE 2

Next, described below with reference to FIG. 10 is the structure of thepixel portion of the element substrate for conducting the inspectionaccording to the invention, which is different from the structure ofExample 1.

A pixel portion 1001 includes source signal lines (S1 to Sx) connectedto the source signal line drive circuit, current feeder lines (V1 to Vx)connected to an external power source of the light-emitting device viathe FPC, gate signal lines (first gate signal lines)(Ga1 to Gay) forwriting connected to the write gate signal line drive circuit, and gatesignal lines (second gate signal lines)(Ge1 to Gey) for erasingconnected to the erase gate signal line drive circuit.

A pixel 1005 is formed by a region that includes source signal lines (S1to Sx), current feeder lines (V1 to Vx), write gate signal lines (Ga1 toGay) and erase gate signal lines (Ge1 to Gey). In the pixel portion 1001are arranged plural pixels 1005 like a matrix. The element substrate ofthis Example can be put into practice in combination with theconstitution of Example 1.

EXAMPLE 3

Described below with reference to FIG. 11 is a method of inspection byusing an opposing detector substrate different from the one dealt within Example 1 for conducting the inspection according to the invention.

In FIG. 11, reference numeral 1101 is a source of electromagnetic wavesfor generating soft X-rays having wavelengths of 0.1 to 100 nm among theelectromagnetic waves, and a power source 1104 is connected to thesource 1101 of electromagnetic waves.

The soft X-rays emitted from the source 1101 of electromagnetic wavesfall on the opposing detector substrate 1102 passing through a fine holeof a shielding plate 1105 corresponding to the object surface. Otherportions are shielded by the shielding plate 1105. The shielding plate1105 is made of a material capable of shielding the soft X-rays to asufficient degree. The soft X-rays pass through the opposing detectorsubstrate 1102 and fall on the air between the opposing detectorsubstrate 1102 and the element substrate 1103. Unlike the opposingdetector substrate 1102 on which the inspection TFT and the opposingdetector electrode are formed for each of the opposing portions formedlike a matrix used in Example 1, the opposing detector substrate 1102used in this Example has an electrically conducting film such as of ametal formed on the insulator so that the whole surface works as theopposing detector electrode. The electrically conducting film needs notbe formed on the whole surface but may be formed in the form of stripesor a mesh.

The opposing detector substrate 1102 can be placed on the elementsubstrate 1103 to conduct the inspection.

As the conductor for forming the opposing detector electrode, there canbe used a metal material which permits the soft X-rays to pass throughhighly efficiently, such as beryllium or aluminum. The shielding plate1105 may be the one that shields the soft X-rays. For example, there maybe used a material which permits the soft X-rays to pass through little,such as lead glass having a hole perforated in a portion through wherethe soft X-rays are to be passed for irradiation.

In this Example, the opposing detector substrate 1102 and the elementsubstrate 1103 positioned under the source 1101 of electromagnetic wavesand shielding plate 1105, are shifted together to irradiate the airpresent between the opposing detector substrate 1102 and the elementsubstrate 1103 with the soft X-rays. That is, the element substrate 1103is interlocked to the opposing detector substrate 1102.

As the air present between the opposing detector substrate 1102 and theelement substrate 1103 is irradiated with the soft X-rays that havepassed through the opposing detector substrate 1102, an electric passageis formed between the opposing detector substrate 1102 and the elementsubstrate 1103, making it possible to measure the current that flowsfrom the pixel electrode possessed by the pixel formed on the elementsubstrate 1103 to the opposing detector electrode formed on the opposingdetector substrate 1102.

Though in the foregoing was described the constitution for inspectingthe element substrate by interlocking the opposing detector substrate1102 and the element substrate 1103 together, it is also allowable tofix them and move the source of electromagnetic waves only.

The measuring method and the evaluation method may comply with those ofExample 1. The constitution of this embodiment can be executed uponcombining the constitutions of Examples 1 and 2.

EXAMPLE 4

Described below with reference to FIG. 12 is a method of inspection byusing an opposing detector substrate different from those dealt with inExamples 1 and 3 in conducting the inspection according to theinvention.

In FIG. 12, reference numeral 1201 denotes a source of electromagneticwaves for generating X-rays having wavelengths of 0.01 to 100 nm amongthe electromagnetic waves, and a power source 1204 is connected to thesource 1201 of electromagnetic waves.

The X-rays emitted from the source 1201 of electromagnetic waves arefocused on the opposing detector substrate 1202 and falls on the elementsubstrate 1203 passing through the opposing detector substrate 1202.Here, the material used for the opposing detector electrode formed onthe opposing detector substrate 1202 may be beryllium or aluminum thatpermits X-rays to pass through highly efficiently.

In this Example, the element substrate 1203 is provided under the source1201 of electromagnetic waves and the opposing detector substrate 1202,and is moved every time when each of the pixels of the element substrate1203 is inspected. The mirror 1205 works to focus the X-rays. That is,in this Example, the source 1201 of electromagnetic waves and theopposing detector substrate 1202 are fixed, and the element substrate1203 is moved every time when a different pixel is inspected.

As the air present between the opposing detector substrate 1202 and theelement substrate 1203 is irradiated with the X-rays, an electricpassage is formed between the opposing detector substrate 1202 and theelement substrate 1203, making it possible to measure the current thatflows from the pixel electrode possessed by the pixel formed on theelement substrate 1203 to the opposing detector electrode formed on theopposing detector substrate 1202. In this embodiment, the X-rays thathave passed through the opposing detector substrate 1202 fall on thepixel that is to be measured on the element substrate 1203 forming anelectric passage at a desired position and making it possible to morecorrectly measure the current.

In the foregoing was described the constitution for moving the elementsubstrate 1203. It is, however, also allowable to conduct the inspectionby securing the element substrate 1203 and by interlocking the source1201 of electromagnetic waves and the opposing detector substrate 1202together. Further, the opposing detector substrate 1202 may be formedlike a ring to permit the passage of the X-rays, or an electrode may besimply provided in the vicinity thereof.

In this Example, the measuring method and the evaluation method are thesame as those of Example 1. When it is difficult to focus the X-ray,however, a mirror having a high reflection factor is provided along theperiphery as required or a capillary plate is provided so that the X-raycan be projected onto a desired position. It is further desired that thedistance is as close as possible between the opposing detector substrate1202 and the element substrate 1203. The constitution of this Examplecan be put into practice being freely combined with the constitutions ofExamples 1 to 3.

EXAMPLE 5

Examples 1 to 4 have dealt with the substrates on which the TFTs wereformed as element substrates. The invention, however, can be put intopractice even by using MOS transistors formed on the semiconductorsubstrate instead of the TFTS. For example, the semiconductor substrate(typically, a silicon wafer) on which the MOS transistors are formed canbe inspected as the element substrate.

According to this Example, the element substrate can be inspected by anyone of the Examples of the invention, the inspection method of Example 3or the inspection method of Example 4.

EXAMPLE 6

Described below with reference to FIGS. 15 and 16 are the cases where aconnector such as FPC or TAB is connected to the display panel of theinvention to ship it as a product.

In FIG. 15, reference numeral 1801 denotes a pixel portion that haspassed the inspection method of the invention, and that is provided withplural pixels.

Reference numeral 1802 denotes a source signal line drive circuit, and1803 denotes a gate signal line drive circuit. In response to selectionsignals output from the gate signal line drive circuit 1803, videosignals output from the source signal line drive circuit 1802 are inputto the specified pixels of the pixel portion 1801. The video signals maybe either digital signals or analog signals. Further, the source signalline drive circuit 1802 and the gate signal line drive circuit 1803 maybe provided in any number.

In this specification, an OLED panel 1807 refers to a module thatincludes a drive circuit constituted by the source signal line drivecircuit 1802 and the gate signal line drive circuit 1803, the pixelportion 1801, and a connector for connecting the wiring possessed by thepixel portion 1801 and for connecting the wiring possessed by the drivecircuit to an external unit. The OLED panel 1807 needs not necessarilybe provided with the drive circuit, and the pixel portion 1801 and thewiring possessed by the pixel portion 1801 may be separately formed.

Here, the OLED panel in which the drive circuit and the pixel portion1801 are provided on the separate substrates and are connected togetherby a connector such as FPC or TAB, is called an OLED panel of theexternally attached type, and the OLED panel in which the drive circuitand the pixel portion 1801 are provided on the same substrate is calledan OLED panel of the integral type. FIG. 16(A) shows an OLED panel ofthe externally attached type, and FIG. 16(B) shows an OLED panel of theintegral type.

FIG. 16(A) is a top view of the OLED panel of the externally attachedtype. The pixel portion 1801 is provided on the substrate 1810, and thewirings possessed by the pixel portion 1801 are connected to the sourcesignal line drive circuit 1802 and to the gate signal line drive circuit1803 formed on the substrate 1812 for external attachment via FPCs 1811.Wirings of the source signal line drive circuit 1802, of the gate signalline drive circuit 1803 and of the pixel portion 1801 are connected toan external unit through the FPC 1812 for external connection.

FIG. 16(B) is a top view of the OLED panel of the integral type. On thesubstrate 1810 are provided the pixel portion 1801, source signal linedrive circuit 1802 and gate signal line drive circuit 1803. The wiringsof the pixel portion 1801, of the source signal line drive circuit 1802and of the gate signal line drive circuit 1803 are connected to anexternal unit through the FPCs 1812 for external connection.

In FIG. 15, reference numeral 1804 denotes a controller having afunction for driving the drive circuit and for displaying an image onthe pixel portion 1801. The controller 1804 works to send signalscontaining image data input from an external unit to the source signalline drive circuit 1802, to form signals (e.g., clock signals (CLK),start pulse signal (SP)) for driving the drive circuit, and works as apower source for feeding a potential to the drive circuit and to thepixel portion 1801.

In this specification, an OLED module 1808 refers to a module thatincludes the drive circuit, pixel portion 1801, controller 1804, pixelportion 1801, drive circuit, controller, and connectors for connectingthe wirings thereof to the external unit. The OLED module 1808 is theone in which the OLED panel 1807 is provided with the drive circuit andthe controller 1804.

Reference numeral 1805 denotes a microcomputer for controlling thecontroller 1804. In this specification, the module including themicrocomputer 1805 and the OLED module 1808 is called OLED module 1809with microcomputer.

In practice, the OLED panel 1807, the OLED module 1808 and the OLEDmodule 1809 with microcomputer are shipped as products. In thisspecification, the OLED panel 1807, OLED module 1808 and OLED module1809 with microcomputer are all regarded as light-emitting devices.

The light-emitting device of this Example can employ the method offabrication and inspection method dealt with in Example 1 and canfurther employ the constitution of pixel portion same as that of Example2. The device can be further inspected by the inspection methoddescribed in Example 3 or 4, and to which can be applied the elementsubstrate of Example 5.

EXAMPLE 7

The invention can be put into practice even when plural elementsubstrates are to be simultaneously formed on a large substrate.

In this case, the drive circuit formed separately from the elementsubstrate, the opposing detector substrate and source of electromagneticwaves may be interlocked together and may be moved on to the elementsubstrate that is to be inspected. Further, the element substrate onlymay be moved to conduct the inspection.

In inspecting plural element substrates, the electric connection must bemade again between the element substrate to be inspected and the drivecircuit for every inspection. The connection terminals on the side ofthe element substrate used in this case may include terminals forinspection. It is, however, also allowable to use terminals that arefinally connected to the external unit through the FPC.

EXAMPLE 8

A light-emitting device formed by implementing examination method of thepresent invention has superior visibility in bright locations incomparison to a liquid crystal display device because it is aself-emission type device, and moreover its field of vision is wide.Accordingly, it can be used as a display portion for various electronicdevices. For example, it is appropriate to use the light-emitting deviceformed by implementing the examination method of the present inventionas a display portion of a display having a diagonal equal to 30 inchesor greater (typically equal to 40 inches or greater) for appreciation ofTV broadcasts by large screen.

Note that all displays exhibiting (displaying) information such as apersonal computer display, a TV broadcast reception display, or anadvertisement display are included as the light-emitting device.Further, the light-emitting device using the examination method of thepresent invention can be used as a display portion of the other variouselectronic devices.

The following can be given as examples of such electronic devices of thepresent invention: a video camera; a digital camera; a goggle typedisplay (head mounted display); a navigation system; an audioreproducing device (such as a car audio system, an audio compo system);a notebook personal computer; a game equipment; a portable informationterminal (such as a mobile computer, a mobile telephone, a mobile gameequipment or an electronic book); and an image playback device providedwith a recording medium (specifically, a device which performs playbackof a recording medium and is provided with a display which can displaythose images, such as a digital video disk (DVD)). In particular,because portable information terminals are often viewed from a diagonaldirection, the wideness of the field of vision is regarded as veryimportant. Thus, it is preferable that the light-emitting device isemployed. Examples of these electronic devices are shown in FIGS. 13 and14.

FIG. 13A is a display for displaying, containing a casing 1301, asupport stand 1302, and a display portion 1303. The light-emittingdevice which is applied the examination method of the present inventioncan be used in the display portion 1303. Since the light-emitting is aself-emission type device with no need of a back light, its displayportion can be made thinner than a liquid crystal display device.

FIG. 13B is a video camera, containing a main body 1311, a displayportion 1312, an audio input portion 1313, operation switches 1314, abattery 1315, and an image receiving portion 1316. The light-emittingdevice which is applied to the examination method of the presentinvention can be used in the display portion 1312.

FIG. 13C is a portion of a head mounted type electrical appliance (rightside), containing a main body 1321, a signal cable 1322, a head fixingband 1323, a screen portion 1324, an optical system 1325, and a displayportion 1326. The light-emitting device which is applied the examinationmethod of the present invention can be used in the display portion 1326.

FIG. 13D is an image playback device (specifically, a DVD playbackdevice) provided with a recording medium, containing a main body 1331, arecording medium (such as a DVD) 1332, operation switches 1333, adisplay portion (a) 1334, and a display portion (b) 1335. The displayportion (a) 1334 is mainly used for displaying image information, andthe display portion (b) 1335 is mainly used for displaying characterinformation, and the light-emitting device which is applied to theexamination method of the present invention can be used in the displayportion (a) 1334 and in the display portion (b) 1335. Note that domesticgame equipment is included as the image playback device provided with arecording medium.

FIG. 13E is a goggle type display device (head mounted display),containing a main body 1341, a display portion 1342, and arm portion1343. The light-emitting device which is applied the examination methodof the present invention can be used in the display portion 1342.

FIG. 13F is a personal computer, containing a main body 1351, a casing1352, a display portion 1353, and a keyboard 1354. The light-emittingdevice which is applied the examination method of the present inventioncan be used in the display portion 1353.

Note that if the emission luminance of EL materials becomes higher inthe future, it will be possible to use the light-emitting device of thepresent invention in a front type or a rear type projector by projectinglight including output images, which can be enlarged by lenses or thelike.

The above electrical appliances are becoming more often used to displayinformation provided through an electronic telecommunication line suchas the Internet or CATV (cable television), and in particular,opportunities for displaying animation information are increasing. Theresponse speed of EL materials is extremely high, and therefore thelight-emitting device is favorable for performing animation display.

Since the light emitting portion of the light-emitting device consumespower, it is preferable to display information so as to have theemitting portion become as small as possible. Therefore, when using thelight-emitting device in a display portion which mainly displayscharacter information, such as a portable information terminal, inparticular, a portable telephone and an audio reproducing device, it ispreferable to drive it by setting non-emitting portions as backgroundand forming character information in emitting portions.

FIG. 14A is a portable telephone, containing a main body 1401, an audiooutput portion 1402, an audio input portion 1403, a display portion1404, operation switches 1405, and an antenna 1406. The light-emittingdevice of the present invention can be used in the display portion 1404.Note that by displaying white characters in a black background in thedisplay portion 1404, the power consumption of the portable telephonecan be reduced. Further, in the case where periphery is dark, it iseffective that the power consumption can be reduced by decreasing theapplied voltage, thereby lowering luminance.

FIG. 14B is an audio reproducing device, specifically a car audiosystem, containing a main body 1411, a display portion 1412, andoperation switches 1413 and 1414. The light-emitting device of thepresent invention can be used in the display portion 1412. Furthermore,an audio reproducing device for a car is shown in Embodiment 8, but itmay also be used for a portable type and a domestic type of audioreproducing device. Note that by displaying white characters in a blackbackground in the display portion 1412, the power consumption can bereduced. This is particularly effective in a portable type audioreproducing device.

FIG. 14C is a digital camera, containing a main body 1421, a displayportion (A) 1422, an eye piece portion 1423, an operation switch 1424, adisplay portion (B) 1425 and a battery 1426. The EL display device whichis applied the examination method of the present invention can be usedin the display portion (A) 1422 and the display portion (B) 1425. Notethat in the case of using mainly the display portion (B) 1425 as anoperation panel, by displaying white characters in a black background,the power consumption of the digital camera can be reduced.

In the case of electrical appliances shown in this embodiment, thesensor portion is provided to perceive the external light and thefunction to lower the brightness of display when it is used in the darkarea as a method to lower the power consumption.

The range of applications of the present invention is thus extremelywide, and it is possible to apply the present invention to electricalappliances in all fields. Furthermore, Embodiment 8 can be implementedin combination of any structures of the Embodiments 1 to 7.

The inspection method of the invention makes it possible to distinguishwhether the element substrate is acceptable or defective even withoutcompleting the element substrate as a light-emitting device or withoutreally effecting the display and, hence, to remove the defective devicefrom the subsequent production process. Accordingly, the cost ofproduction is decreased and the yield is improved.

1. A device for inspecting element substrates comprising a source ofelectromagnetic waves and an opposing detector substrate, the source ofelectromagnetic waves ionizing a gas present between the opposingdetector substrate and an element substrate that is to be inspected,wherein the opposing detector substrate has a TFT and an electrodeconnected to the TFT.
 2. A device according to claim 1, wherein thesource of electromagnetic waves generates electromagnetic waves orX-rays of a wavelength of from 0.01 to 100 nm.
 3. A device according toclaim 1, further comprising an ammeter for measuring an electric currentbetween the opposing detector substrate and the element substratethrough the ionized gas.
 4. A device according to claim 1, wherein theopposing detector substrate has an opposing detector electrode.
 5. Adevice according to claim 4, wherein the opposing detector electrode ismade of a conductor that permits the transmission of electromagneticwaves or X-rays of a wavelength of 0.01 to 100 nm.
 6. A device accordingto claim 5, wherein the opposing detector electrode is made of berylliumor aluminum.
 7. A device according to claim 1, wherein the opposingdetector substrate has plural TFTs and plural electrodes connected tothe TFTs.
 8. A method of inspecting element substrates by measuring anelectric current between the element substrate and an opposing detectorsubstrate through the ionized gas by using a device according to claim1, thereby to inspect the current-flowing state of the pixel electrodesof the element substrate.
 9. A method of inspecting element substratesby emitting electromagnetic waves from a source of electromagnetic wavesin order to ionize a gas between an opposing detector substrate and anelement substrare to be inspected, wherein the opposing detectorsubstrate has a TFT and an electrode connected to the TFT.
 10. A methodaccording to claim 9, wherein the source of electromagnetic wavesgenerates electromagnetic waves or X-rays of a wavelength of 0.01 to 100nm.
 11. A method according to claim 9, wherein a current is measuredbetween the opposing detector substrate and the element substratethrough the ionized gas.
 12. A device for inspecting element substratescomprising a source of electromagnetic waves and an opposing detectorsubstrate, the source of electromagnetic waves ionizing a gas presentbetween the opposing detector substrate and an element substrate that isto be inspected, wherein the opposing detector substrate has an opposingdetector electrode, and wherein the opposing detector electrode is madeof a conductor that permits the transmission of electromagnetic waves orX-rays of a wavelength of 0.01 to 100 nm.
 13. A device according toclaim 12, wherein the source of electromagnetic waves generateselectromagnetic waves or X-rays of a wavelength of from 0.01 to 100 nm.14. A device according to claim 12, further comprising an ammeter formeasuring an electric current between the opposing detector substrateand the element substrate through the ionized gas.
 15. A deviceaccording to claim 12 wherein the opposing detector electrode is made ofberyllium or aluminum.
 16. A device according to claim 12, wherein theopposing detector substrate has plural TFTs and plural electrodesconnected to the TFTs.
 17. A device for inspecting element substratescomprising a source of electromagnetic waves and an opposing detectorsubstrate, the source of electromagnetic waves ionizing a gas presentbetween the opposing detector substrate and an element substrate that isto be inspected, wherein the opposing detector substrate has an opposingdetector electrode, and wherein the opposing detector electrode is madeof beryllium or aluminum.
 18. A device according to claim 17, whereinthe source of electromagnetic waves generates electromagnetic waves orX-rays of a wavelength of from 0.01 to 100 nm.
 19. A device according toclaim 17, further comprising an ammeter for measuring an electriccurrent between the opposing detector substrate and the elementsubstrate through the ionized gas.
 20. A device according to claim 17wherein the opposing detector electrode is made of a conductor thatpermits the transmission of electromagnetic waves or X-rays of awavelength of 0.01 to 100 nm.
 21. A device according to claim 17 whereinthe opposing detector substrate has plural TFTs and plural electrodesconnected to the TFTs.